Elevated joint contact stress from residual articular incongruity following intra-articular fracture (IAF) is a critically important risk factor for post-traumatic OA (PTOA) that until recently could not be assessed, presenting a major obstacle to meaningful research aimed at improving treatment. The goals of the proposed research are to employ a clinically applicable measure of contact stress, obtained using computational discrete element analysis (DEA) methods, to diagnose patients at risk of PTOA following IAF and to develop and test methods of preventing elevated contact stress from joint incongruity. In retrospective studies of different lower extremity joints, DEA will be utilized to identify thresholds of joint contact stress above which PTOA is most highly likely (Specific Aim 1). To advance understanding of how elevated cumulative contact stress after IAF affects joint structure and biology to cause PTOA, prospective studies will be undertaken to correlate contact stress levels with morphologic articular surface changes detected on MRI, with alterations in serum and urine biomarkers, with radiographic changes, and with patient pain and function (Aim 2). The other two aims of this study will make important clinical steps to prevent elevated contact stress following IAF and thereby improve patient outcomes. New intra-operative techniques will be developed to assess the contact stress exposure associated with a given candidate IAF reduction during operations, to inform surgeons in their decision-making. These novel techniques will be based on deduced fragment poses from fluoroscopic images correlated with pre-operative CT models; contact stress estimates will be calculated with DEA. These techniques will be assessed on simulated fracture models and piloted in the operating room during IAF surgery and compared with conventional treatment (Aim 3). In a pilot clinical feasibility study, acute joint distraction using a ring fixator for severe tibial pilon fractures will be assessed using DEA, MRI and biomarkers to determine if temporarily sparing damaged articular surfaces from harmful joint contact stress after injury improves joint healing in such high energy IAFs (Aim 4).